The following invention relates in general to the field of positioning systems and more specifically to positioning systems for semiconductor testing and inspection systems.
Semiconductor manufacturing and testing often requires precise positioning of semiconductor wafers with respect to manufacturing or testing equipment. Positioning systems are often used to move and hold semiconductor wafers in proximity to testing or manufacturing equipment. Optical scanning or imaging techniques often involve scanning very small portions of a semiconductor wafer and then combining all of the scanned portions to obtain an image of the entire wafer. Such a technique typically requires moving either the wafer or the imaging device to obtain each individual image. In this type of testing, precise positioning of a semiconductor wafer with respect to a testing device is particularly important.
As a general matter, as semiconductor manufacturing techniques have advanced, devices on semiconductor wafers have become increasingly small. As device sizes decrease, accurately inspecting the devices becomes increasingly difficult. Also, as semiconductor devices decrease in size, the density of devices within a given area of a semiconductor wafer increases. Accordingly, in order to inspect the same number of wafers in a given period of time, an inspection system often must record a greater number of measurements. Often, this requires a positioning system to move more frequently in order to inspect the increased number of devices in a shortened period of time. Increased movement of the inspection system can lead to a number of difficulties related to dynamic forces acting on a positioning system affecting the accuracy and efficiency of the semiconductor testing system.
Another consideration in any semiconductor manufacturing process is that any slowdown or bottleneck within the process can be extremely costly. Routine maintenance operations such as equipment adjustment or replacement may cause significant delay, consuming the valuable time of skilled technicians and interrupting a semiconductor manufacturing process. Such an interruption can be extremely costly, negatively effecting throughput.
Semiconductor inspection systems, particularly systems that inspect systems optically, are often sensitive to inaccuracies in wafer positioning. If wafers that are being tested are not positioned correctly, testing may be ineffective and lead to erroneous results. Inaccurate positioning may also lead to difficulties in assembling multiple images of portions of a wafer into a single, useful, image of an entire wafer.
Therefore, a need has arisen for a positioning system that facilitates the accurate positioning of wafers for inspection and testing.
A further need has arisen for a positioning system that facilitates frequent movement of a wafer.
A still further need has arisen for a positioning system that facilitates maintenance and removal operations.
In accordance with teachings of the present disclosure, a system and method are described for positioning a wafer within an inspection system that reduces the problems associated with prior systems and methods for positioning wafers.
The present invention discloses a positioning system that includes at least three positioner assemblies. Each positioner assembly includes a housing with a coarse adjustment assembly and a fine adjustment assembly disposed within the housing. The positioner assemblies are releasably coupled to a wafer chuck and operable to selectively position the chuck. More particularly, the fine adjustment assembly includes a piezoelectric actuator that is selectively movable between a retracted position and an extended position.
The coarse adjustment assemblies may include a spherical ball disposed within the housing adjacent to the wafer chuck. The spherical ball may move vertically to selectively position the wafer chuck. A plunger may be disposed within the housing adjacent the spherical ball and be selectively positionable by an adjustment screw.
The system may also include a locking spring that interfaces with the wafer chuck and the housing such that the locking spring loads the interface between the wafer chuck and housing. An over-center spring tensioner may be disposed within the housing to selectively interface a portion of the locking spring and selectively load the locking spring.
The present invention provides a number of important technical advantages. One technical advantage is providing positioner assemblies with coarse adjustment and fine adjustment assemblies. The positioner assemblies facilitate accurate positioning of a wafer secured on the wafer chuck.
Another important technical advantage is providing a locking spring that loads the interface between the housing and the wafer chuck. The loading interface allows the wafer chuck to maintain stability during frequent movement.
Another important technical advantage of the present invention is providing an over-center spring tensioner for interfacing the locking spring. Providing the over-center spring tensioner facilitates the removal of the wafer chuck for maintenance or replacement.